I had an experience with one of the businesses that you listed back in the mid-2000s that I only recently found out how bad the repair was. It was a pretty obscure amp that we had in for repair - and they did work on our other amps that was good, so I do not want to call them out to turn business away from them.
There is no way to prove it as it happened when I was really young, so part of this due to my own naivety in trusting people.
This shop had our amp for nearly a year and when we got it back it didn't work (turned on and played crazy squeaky feedback noises with and without a guitar plugged in) and then they took it back for almost another half year until they finally gave it back to us... and it although it was now working, it just didn't sound the same.
I now know this is because we received a 2001 reissue replacement head in our cabinet - the amp we had was a '94 that we had purchased used from L&M in '99. The serial # on this head is for a 2001, though the cab it sits in as well as the speakers are date stamped for '94.
Unfortunately I will never know the reason for this happening - whether the amp was accidentally damaged beyond repair while they had it, if it was swapped because someone really liked it (it was a fantastic amp), or they just couldn't repair it and thought this an actual solution. It does not matter because I will not use them again and ultimately wish they had just been honest with me had it been an accident or due to inexperience with this amp.
As I said - I won't name the business, because honestly they did some work for us that was decent. That said they do have some reviews online that echo hints of what I experienced with this one repair - and if anything I hope that someone takes away from this post to always keep track of your serial #s and gear when you are taking it in for repair, not every business is honest.
